1. Field of the Invention
The present invention relates generally to screeds and strike-offs for placing, screeding, finishing and shaping plastic concrete. More particularly, the present invention relates to a dynamic system for concrete tools that can be selectively extended or retracted to avoid obstacles.
2. The Prior Art
As recognized by those skilled in the concrete finishing arts, after concrete is initially placed during construction, the upper surface must be appropriately finished. The purpose of this finishing is to give the concrete a smooth, homogeneous and correctly textured surface and appearance. Various finishing devices, including screeds, have long been in use throughout the industry for treating plastic concrete. Known prior art systems include "bull" floats, finishing boards, strike-offs, pan floats, plows, blades and the like;
Strike-offs contact rough, freshly placed plastic concrete with a rigid leading edge to initially form and grade fresh concrete. Bull floats essentially comprise a flat wooden board attached to a handle, much like a broom handle. These floats are intended to be manipulated by a single worker. Screeds are elongated tools employing a leading strike-off blade and one or more floats secured to a framework. These screeds allow several finishing steps to be accomplished in a single pass. Forms constrain the concrete until it is set. They may also provide a working support for the typical screed or finishing machine.
The selection of blade design for a particular screed is based upon a variety of factors, such as the characteristics of the concrete being laid. Variables relating to concrete finishing result from the selection of the type and percentage of aggregate, sand, cement, ad-mix and water. Temperature, slab thickness, slump and placement method also vary the application procedure. Those skilled in the art will recognize that the selected finishing equipment must be appropriately matched to the job demands. Thus in screeding, for example, an optimum blade must be chosen based on the condition of the concrete. If high slump concrete is to be screeded, a floating pan would be ideal. For finishing drier concrete, a heavier twin-bladed screed might be more desirable. In all cases it is desirable to provide a method for automatically insuring level finishing.
It is an established fact in the art that vibration facilitates concrete finishing and consolidation. Many vibrating systems are presently in use in the industry. Vibration during screeding helps to settle or consolidate the concrete, thus eliminating air voids. Also, it helps to densify and compact the concrete during finishing. Vibrational screeding also draws out excess water, thereby increasing the cured strength of the placed concrete. A fine layer of component cement and sand aggregate is raised to the surface by vibration along with the excess water. This slurry aids in the subsequent fine finishing of the concrete, promoting the attainment of a uniform product.
I hold several patents in the art of concrete placement and finishing. One such is a prior art, self-propelled "triangular truss" screed that rides upon the aforementioned forms, namely U.S. Pat. No. 4,349,328. Additionally, U.S. Pat. No. 4,798,494 discloses a floating vibratory screed that finishes concrete with or without forms. Finally, prior Allen U.S. Pat. Nos. 4,316,715; 4,363,618 and 4,375,351 and the various references cited and discussed therein are germane to the general technology discussed herein. All the above patents have been assigned to the same assignee as the present case.
U.S. Pat. Nos. 4,650,366 and 4,386,901 disclose screeds capable of formless, self-supporting or floating operation. The latter patent speaks to a relatively heavy triangular truss screed adapted to be operated by two workmen without the use of forms. U.S. Pat. No. 4,650,366 discloses a light weight, portable vibrating screed including a central, extruded beam element.
U.S. Pat. No. 3,431,336 discloses a vibrating finishing screed adapted for use upon plastic concrete that apparently is capable of floating. U.S. Pat. No. 2,314,985 discloses a vibratory hand screed including a central, vibrated pan that is apparently adapted for use upon plastic concrete without support upon confining forms.
Other prior art screeds, generally of the "form-riding" type, include those screeds disclosed in U.S. Pat. Nos. 4,340,351; 4,105,355; 2,651,980; 2,542,979; 3,095,789; 2,693,136; and 4,030,873.
Stilwell, U.S. Pat. No. 4,427,358, discloses a coupling for eccentrically weighted driveshafts for vibratory screeds. This coupling employs a spring biased collar to captivate and join two semicylindrical shaft segments.
An important consideration in planing any job is not only the tools to be used in finishing the concrete but the manpower and logistics of carrying out the work. Concrete must often be placed and finished in relatively confined spaces. For example, the floors within a building are often placed after the majority of the structural elements of the building. Therefore, a contractor may well find it necessary to finish a hallway floor or a floor within a room after the erection of several disruptive structural elements. Oftentimes open areas are interrupted by structural members such as columns or other similar protrusions. Screeds known in the art are generally convertible in length only by breaking the screed down and removing or replacing sections.
Therefore, it is desirous to provide a screed that readily clears obstacles without adding or adjusting sections. It is further advantageous to provide a screed that can bypass columns and obstructions during finishing operations. It is necessary that the bypass readily lock in a deployed position in axial alignment with the rest of the screed and its elements (i.e., strike-off, pan float and/or bull float). The bypass needs to be vibrated when the main sections are vibrated. Therefore, the vibration system of the main screed section must interconnect with the bypass. In the case of screeds vibrated by an eccentrically weighted shaft, the vibrating bypass shaft must be connected to the main screed shaft.